The four-stroke engine has powered cars for more than a century. Intake, compression, power, exhaust. It is simple, steady, and everywhere.
Mazda, however, now wants to change that. The company has filed a U.S. patent for a six-stroke engine. It does not only burn gasoline. It breaks the fuel apart, makes hydrogen, and burns that as part of the cycle. The aim is simple yet massive: cut carbon.
The new strokes
The cycle starts the old way. Intake, compression, power. But the spent gas does not go out the pipe. It is pushed into a third port, into a chamber Mazda calls a decomposer.
There the heat and a catalyst break down a small shot of gasoline. The hydrogen is saved. The carbon turns solid.
Two more strokes follow. One pushes the hot gases into the decomposer. One pulls them back. Then the exhaust stroke clears the cylinder. The hydrogen feeds the engine as its new fuel. The carbon stays trapped inside until it can be removed.
The hard part
Thermal cracking is not easy. It needs heat between 400 and 800 degrees Celsius (752 and 1,472 degrees Fahrenheit). It needs a catalyst that can survive it. Mazda does not say which one.
The carbon is another problem. A gallon of gasoline carries about five pounds of carbon. Store fifteen gallons and you have eighty pounds of solid waste. Mazda’s patent allows for a purge system but does not say how often it must be emptied.
One may wonder what happens to the carbon. The patent shows a purge line to clear the decomposer when buildup occurs. Mazda does not say how often it must be emptied. In theory, the carbon is pure and could be used in steel, pigments, or other industries. But that is not part of the plan.
The engine also loses power in six-stroke mode. The patent suggests pairing it with an electric motor to make up the difference. That adds weight, cost, and parts.
The claims
Mazda says the system could run with “no carbon oxides” in the exhaust. That is unproven. Hydrogen burns clean, but at high heat it can still make nitrogen oxides. The patent is silent on this.
No data is given on efficiency. It is unclear if the energy lost in breaking down gasoline is made up for by the cleaner burn. The total system, with all its moving parts and heat, may be less efficient than a simple gasoline engine.
The odds
In 2023, battery electric vehicles made up about 18 percent of global sales, according to the International Energy Agency. Gasoline cars still held around 70 percent. Billions of them remain on the road.
Mazda’s idea is a bridge: use the pumps we have, trap the carbon before it leaves, and burn the hydrogen made inside the car.
The promise is wide. The doubts are wider. No one knows yet if this six-stroke can make enough hydrogen fast enough, or run strong enough, to matter. What will it cost to build? How will it rate in power? Can it run clean over time, or only in the lab? A patent is not a car. It is an idea drawn on paper, waiting to prove itself in steel. Mazda may have sketched the future, but the road to it is long.
Mazda has a history of odd engines. It kept the rotary alive for decades. It built Skyactiv-X, a gasoline engine that fires from compression like a diesel.
Now it offers a six-stroke. At a time when the world is building batteries and chasing range, Mazda still plays with pistons and heat.
It may never leave the patent office. It may fail under heat and weight and cost. But it shows something else. Mazda is not done with the engine.
And maybe the engine is not done with us.